Variable electrical resistance device



Dec. 31, 1935. w, THOMPSON 2,026,405

VARIABLE ELECTRICAL RESISTANCE DEVICE Filed septa 15, 1954 Inventor: Louis W 'Tho psoh Patented Dee. 31, 1935 i 2,026,405

UNITED STATES PATENT OFFICE AVARIABLE ELECTRICAL RESISTANCE DEVICE Louis W. Thompson, seheneetady, N. Y., assigner to General Electric Company, a corporation of New York Application September 13, 1934, Serial No. 743,850

22 Claims. (Cl. ,Q01-5l) My invention relates to variable electrical reis reduced substantially to' zero, while when the sistance devices and more particularly to compressure applied to the device is low, correpressible type variable electrical resistance desponding to the maximum resistance position of vices. the device, the engagement of the elements com- This application is a continuation-impart of prising the device will be suftlciently firm to in- 5 my application Serial No. 604,954, iiled April 13, sure stable and reliable operation at this position. 1932 and assigned to the assignee of thepresent I obtain a 'part of the change in resistance by application. constructing the units with high and low specic Compressible type variable resistances, of resistance sections, as will be more fully delo which the well known carbon pile resistance is scribed hereinafter. l0 perhaps the best known example, possess a num- An Objeet Of my inVeniiOn iS t0 liOVide en ber of distinct operating advantages. Among improved type of compressible resistance. these advantages are the ability of such vari- Another Object of my invention iS i0 Provide able resistance devices to vary their resistance a compressible pile resistance having an inw in infinitely small steps and their ability to creased range of resistance Venetien. do this without the use of circuit making andA A further Object 0f my inventin iS i0 provide breaking contacts. Heretofore. however, these a novel unit for compressible type eSiSiellCeS- devices have had certain inherentI operating An additional object of my invention is to limitations which have militated against their DIOVide a COmDIeSSible Dile type resistance Whieh more wide-spread use. These operating limihas a substantially zero resistance through the 2u tations are those which affect the operation of units comprising the Dile When full pressure iS the devices when they are operating at their applied thereto. maximum azi-:1 minimum resistance limits, My invention Will be better understood lfrom Thus it; has been found that ai; the maximum the following description taken in connection e5 resistance limits of the operation of compressible with the accompanying drawing and its scope 2e pile resistances, these devices become relatively will be pointed out inthe appended Claims. `unstable and extremely sensitive to vibration, due In the drawing, Fig. 1 is a side elevation of a to the fact that the pressure tending to force Particular type of resistance unit for my corn-a the contact faces of the units ofntne piles topressible resistance; Fig-21s a plan view Vof the to gether is comparatively low. In their other exunit shown in Fig. 1; Fig. 3 is an elevation, partly 3o treme condition of operation,` that is to say, in section, of a manually controllable compreswhen it is desired to have the pile resistances Sible Dile resistance employing resistance units have a minimum resistance,=it has been found of the type illustrated in Figs. i and 2; Figi that even when an, excessively high pressure illustrates diagrammatically how a compressible is applied to the pile resistances, they will have Dile IeSiSGenCe may be used as an element of 35 an appreciable resistance. For gree'est usefulan automatic regulator; Fig. 5 is a sectional ness, however, it is desirable that these resist-4 View of a modified unit; and Fig. 6 is a plan view ances be able to have a .minimum resistance 0f the unit ShOWn in Fig- 5. value which is substantially zero. Heretofora In Figs. l and 2, I. have illustrated one embodit@ it; has only been possible to have this result by ment of my invention in a particular form of using a special external contact arrangement resistance unit which is adapted for use in comfor short-circuiting the resistance when full pressible pile resistanees. An important dispressure is applied thereto. tinguishing characteristic of this unit is that In accordance with my invention I provide a it is composed of a resilient, or elastic, resistance @E5 compressible resistance which is built up of novel material l. One such material which is suitable 45 units and which is stable and satisfactory in for use is carbon, although my invention is not operation at its maximum resistance values and limited to any particular type of material, and which has a substantially zero resistance at its metal plates, or discs, having an oxide coating other extreme limit of operation. One way that may be employed, if desired. It is also import- 5@ I achieve these desired results is by building up ant that the adjacent, or cooperating, contact 50 a compressible pile resistance from a plurality faces of the units comprising my compressible of units, some of which may be elastic and deresistance be not normally parallel and one way iormable in such a manner that when full pres- 'of insuring this is to make at least one of the sure is applied to the device the electrical resistopposite contact faces of each unit curved. As ance through the units comprising the device shown in Fig. 1, I have shown both the top and .5,5

ness of the unit, as measured between parallel planes, represented in one instance by the lines 2 and 3, varies, it being thickest at its ends and thinnest at its center. However, my'invention is not limited to such a shape and as the description of my invention proceeds it will become obvious to those. skilled in the art that the top or bottom, or both, contact surfaces may be any shape.

I connect electrically, by means of a comparatively low resistance path, the portions of the top and bottom faces of the unit which are at. its thinnest points. This effective short-circuiting may be done in anyconvenient manner and, as shown, I employ a coating fl of'metalforming a ring about the thinnest portion of the unit. In effect, the coating' vforms a relatively low resistance section of my unit. The metal coating may be applied in any suitable manner, such as by electroplating or by pressing thin metal foil on the unit, although I have found `that best results are obtained when the metal is volatilized and is sprayed onto the material I by pressure through a nozzle. Any suitable metal may be employed and I have found that good results are obtained when silver is used.'

' As I intend that theI unit be flexed when pressure is applied thereto, it is desirable to cut certain portions out of the unit and I have found 'that particularly good results are obtained when V-shaped notches are cut out o f the ends of the unit between its-top and bottom faces. These 35 notches are illustrated at 5 in Fig. 1.

As shown in Fig. 2 the unit is of an elongated rectangular shape, but this is not important and it may have any desired shape.

In the manually controlled compressible pile resistance illustrated in Fig. 3 there is provided a suitable base 6 on which are mounted end supports 'I, for the pile, and these supports are provided with suitable binding posts 8. The bases is preferably made of insulating material while supports 'I are made of any conducting material. Between the supports is mounted a tubular insulating member 9. Fitted loosely in this container are a plurality of the units shown in Figsl 1 and 2 and these units are so arranged inv the container that their contact faces are mounted for cooperation and are adjacent each other.

',A suitable means, in the form of a hand screwy li), is employed for applying pressure to the unit.`

In operation, as the hand screw I0 turns in a wayto increase the pressure on the pile the tips fof the units will first come into contact. By

giving the screw I0 a slight turn all of the. units may be held rmly together. due to the slight exing of the legs of the V-shaped notches. The

j current path will be from the right-handbinding post lthrough support 1, through screw I0,

a conducting plate II, and then in a zigzag path through all of the units' to the other supporting member 'I and to the other binding post.' The resistance will be `relatively high for three separate distinct reasons. These are that vthe electrical path is considerably longer than the short- .est distance between the end units because of the fact that the conducting path is zigzag in shape; the area of contact ofthe units is relatively small as justthe tips of the units are in contact; and as the units are only veryslightly composed of carbon, be high.

compressed, and as they are the resistance ofthe material itself will vbottom contact faces of the unit to be dished; inwardly, or concave, so that the effective thick-A Of course, if a material whose resistance does not change with pressure is used, the latter factor will not be present. If the pressure on the pile is increased, by continuing to turn the screw I0, the units will flex further and theA points of contact of the units will move toward their centers,

thus s1multaneous1y shortening the conducting path, increasing the contact area of the units,

and decreasing the resistance of the units due to the increase in pressure applied thereto.- When full pressure is finally applied to the pile substantially all of the cooperating contact faces of adjapent units will be in contact with the result that the sections, or portions, 4, of the units will be in 'contact thereby providinga substantially zero resistance path through the entire pile.

From the above description of the operation of a particular embodiment of my invention it will be seen that, in principle, the operation of my'invention depends upon the use of at least one resilient, elastic or deformable element, which may or may not be a resistance element, cooperating with a resistance element, which may or may not be deformable, the resistance element l having a substantially zero resistance section between opposit'e contact faces, which section is arranged to come into engagement with the adjacent element when full pressure is applied to In the automatic regulating arrangement` shown in Fig. 4 a compressible pile resistance, composed of my units, is connected in series with the eld winding I2 of a generator I3 which is connected to energize a circuit I4. A voltage responsive electromagnet I5 which is connected across the circuit I4 is arranged, by means of a suitable linkage I6 to control the pressure on the pile I I. In this manner when the voltage of the generator I3 increases above a predetermined normal value the pull of the magnet I5 increases in such a manner that this magnet operates to reduce the pressure on pile I I thereby increasing its resistance and thus decreasing the current in the eld winding I2. This decreases the voltage of the generator I3 and returns it to normal.y Similarly, if the voltage of -generator I3 de creases below normal for any reason the magnet I5 will have its pull weakened, thereby to increase the pressure on the pile II with the result that its resistance is decreased and the ,current through the field winding I 2 is increased, thereby increasing the voltage of the generator I3. This will continue until the voltage returns to normal.

In the modification shown in Figs. 5 and 6 the resistance between the opposite contactl faces of the middle portion of the unit is short-circuited by an electrical conductor in the form of a atheaded rivet I1 passing through the unit and having a washer I8 riveted thereto. Parts I1 and I8 may be made of silver, if desired, and in a pile comprising a plurality of the units shown in Figs. 5 and 6, when full pressure is applied thereto and the units are compressed suiiiciently, all of theA conducting members I1 will come into contact thereby in effect, short-circuiting the entire device Y .that the construction is more ruggedand reliable in that the metal coating might sometimes break of! or rub thin enough to provide a relatively poor conducting path. However, the relatively rugged and large cross-section member I1 insures a rela.- tively low resistance conductor between opposite contact faces of the unit.k

While I have shown and described a particular embodiment of my invention, ltwill be obvious to those skilled in the art that changes and modifications may be made without departing from my invention and I, therefore, aim in the appended claims to cover all such changes and modlicationsas fall within the true spirit and scope of my invention,

`What I claim as new and desire to secure by Letters Patent of'the United States, is:

l. A unit for a`compressible resistance, said unit permanently having electrically parallel high and low specific resistance sections respectively between opposite contact faces. 2. A unit for a compresslble resistance, said unit having two external contact faces between whichA there is a relatively high resistance, and means havingk a relatively low specific resistance permanently connecting portions of said faces.

3. A unit for a compressible type variable resistance, said unit having two contact faces between which there is appreciable resistance, and

means for permanently short-circuiting the re.

sistance between hired portions of said faces.

4. A resistance unit for a pile type resistance. said unit having opposite external faces between opposite points of which there is an appreciable electrical resistance, and a metal coating on said unit for electrically connecting portions of said opposite faces of said unit.

'5. A unit for ja compressible pile resistance, said unit having opposite external faces of which one is concave, and a relatively low specific resistance electrical conductor joining the center portions of the said faces.

6. A unit for a compressible pile resistance, said unit having a non-uniform effective thickness and a relatively low specific resistance conductor joining the portions of itsl external faces at the place of minimum thickness.

'1. A unit for a compressible pile resistance, said unit having opposite external faces between which its effective thickness varies as measured between parallel plane surfaces, the portions of vsaicl'faces between which the eective thickness of said unit is a minimum being electrically con nected by a relatively low specific resistance electrical conductor.

8. A resistance unit for pile type resistances, said unit having a pair of external contacteurfaces one of which is progressively deformable into a given'shape by the application of pressure to said unit, anda substantially zero resistance conductingg path connecting the portions of said deformable contact surface which last conform to said given shape with the other contact surface.

9. A resistance unitfor compressible type ref sistances, said unit being composed of resilient resistance material having a pair of opposite external contact surfaces one of which is progressively deformable' into a given shape by the application of pressure to said unit, and a sub'- stantially zero resistance conducto;` connecting the portions of said deformable contact surface which last conform to said given shape with the other contact surface.

10. An elongated carbon .pile plate, said plate having opposite faces of which one is concave, :5 and a band of relatively low resistance material encircling said plate at its middle portion.

11. A rectangular carbon plate having a pair of opposite contact faces, one of said faces being concave, and a ring of metal coating encircling 10 said plate at its middle portion.' l

. 12. A compressible resistance device comprising a plurality of deformable units each having high and low specinc resistance sections between opposite 'contact faces, said units having normally le' lnon-parallel adjacent contact faceaand'means for compressing said umts in such a manner that at low pressure the high specific resistance sections are in contact with each other while the low specific resistance sections are out ofcontact 2@ with each other and at high pressure the low specific resistance sections are in contact with each other.

13. In combination, a plurality of electrical conducting elements arranged in a pile, said ele- 25,

ments having normally non-parallel cooperating contact faces, one of said elements being`composed of elastic material, one of said elements being composed of electrical resistance material, means for applying pressure to said pile whereby 3@ said elastic element is deformed in Suche. manner that the cooperating contact faces are progressively brought into substantially complete ensagement, and a relatively low specific resistance electrical conducting means connecting the portions of the opposite contact faces of said element of resistanceinaterial which are substantially the last to come into engagement with cooperating contact faces.

14. A variable resistance device including, in 40 combination, a plurality of electrical conducting plates arranged in a pile, said plates having normally nonparalleladiacent contact faces, one of said plates being composed of deformable resistancematerlai, means for applying pressure to said pile in such a manner that the opposite contact faces of said deformable plate come progressively into substantially complete contact with their adjacent contact faces, and relatively low specific resistance electrical conducting means connecting 5@ nation, a plinality of carbon plates arranged in a pile, said plates havingnormally non-parallel cooperating contact faces, means forv applying pressures to said pile whereby said plates are progressively deformed until the cooperating contact faces thereof are in substantially complete c@ contact, and relativeLv low specific resistance electrical r conducting means connecting `the points on opposite faces of each plate which'are the lastpointsofsaidfacestocontactwithw operating faces. 55

16. A resistance unit for a pile type resistance, said unit having opposite external faces between opposite points of which there is anl appreciable electrical resistance, and a metal conductor extending through said unit from one of said faces to the other, the ends of said conductor forming parts of saidcontact faces.

17. A carbon resistance unit for a compressible pile type resistance, said unitl having opposite external contact faces betweenv which there, is-an f appreciable electrical resistance, and a relatively low specific resistance fiat-headed metal rivet passed through said unit between said contact faces.'4

18. An elongated carbon pile plate, said plate having opposite contact faces of which one is concave, and a relatively low specic resistance metal conductor which is passed through said plate between said faces at the middle portion thereof.

19. A rectangular carbon plate having a pair of ppos te contact faces, one of said faces being concave, and a silver rivet passed through said plate between said faces at the middle portion thereof.

20. A pile type variable resistor comprising a plurality of resistance `units having portions of adjacent contact faces out of contact with each other when minimum preure is applied to said pile, separate relatively low vresistance conducting means carried'by each of said units for interconnecting the out of contact portions of their respective contact faces, and means for applying pressure to said pile so that said separate low resistance conducting means are brought into contact with each other.

2 1. A pile type variable resistor comprising a plurality of resistance units of the same relatively high contact resistance material having portions of adjacent contact faces out of contact with each other when minimum pressure is'ap- 5 plied to said pile, separate relatively low resistance conducting means carried by each of said units for interconnecting the out of contact por,- tions of their respective contact faces, and means for applying pressure to said pile so that said 10 separate low resistance conducting means are brought into contact with each other.

22. A variable resistance 'comprising a pile of carbon resistance units having portions of adjacent contact faces out of contact with each other 15 when relatively low pressure is applied to said pile, separate relatively low resistance-conducting means passed through each of said units between the out of contact portions of their respective contact faces, and means for applying pressure to said pile so that said separate low resistance conducting means are brought into contact with each other.v

mors W. THOMPSON.- 25 

